Subject: [Sipping] Resume support for MSRP file transfer

From: "Juuso Lehtinen" <[email-masked]>
Date: Mon, 5 Jun 2006 11:35:41 +0300

Hello all,

I-D draft-garcia-sipping-file-transfer-mech-00.txt describes how MSRP
file transfer sessions can be set up using SIP. However, the draft
does not specify how to resume partially completed file transfers.

I think it is important to have a way to continue a partially complete
file transfer without starting the transfer from the beginning;
especially if the file being transferred is large and/or the
end-to-end path capacity is small (e.g., transferring files in mobile
environment).

Two alternatives to implement resume support for file transfers:

(1) Signal position in file using MSRP
-Can be used with any session establishment protocol
-Requires additional MSRP messages to the beginning of the session

(2) Signal position in file in SIP/SDP
-No need to modify MSRP
-Requires a new SDP attribute; e.g., filetransfer-pos

At this point, I think that the alternative (2) would be a better
choice because it requires the least modifications to existing
protocols.

Any thoughts?

BR,
 Juuso Lehtinen

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From: Miguel Garcia <[email-masked]>
Date: Fri, 30 Jun 2006 08:59:30 +0300

Hi Juuso:

Thanks for your comments. Please notice that the draft is not targeting 
the MMUSIC WG, since it just extends SDP and the SDP offer/answer model.

http://www.ietf.org/internet-drafts/draft-garcia-mmusic-file-transfer-mech-00.txt

I acknowledge your requirement, I think it is very important that we add 
this function to resume file transfers...

So... I believe MSRP does not provide a mechanism to move the pointer of 
the file to start a transfer from a position different than zero. So, 
most likely, we need to go to option 2 and put there something like a 
byte ranges.

/Miguel

-- 
Miguel A. Garcia           tel:+358-50-4804586
sip:[email-masked]
Nokia Research Center      Helsinki, Finland